JP2538121B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus for obtaining a high quality recorded image.

(Prior Art) Conventionally, a binary dither method has been often used as an image forming apparatus for recording a halftone image in an electrophotographic printer or a thermal transfer printer having insufficient gradation reproduction.

(Problems to be Solved by the Invention) However, in the device configuration to which the above-mentioned conventional binary dither method is applied, a large size dither matrix must be used in order to obtain sufficient gradation, resulting in a reduction in resolution. In addition, there is a problem that image quality is deteriorated such as generation of moire due to interference between halftone dots of a document and a dither pattern.

A multi-valued dither method has been proposed in order to improve the above-mentioned problems. However, since an intermediate density level is used in one pixel, density unevenness of a recorded image is likely to occur, and there is a limit in improving image quality.

Therefore, an object of the present invention is to provide an image forming apparatus capable of solving the above conventional problems.

(Means for Solving the Problem) To this end, the present invention provides an image forming apparatus that performs gradation recording by changing the size of each dot based on input image data. Has a plurality of different conversion characteristics for converting the density level of the image data into a density level for dot recording, and one of the plurality of conversion characteristics is that the dot recording is performed when the density level of the image data is a low density level. Conversion processing means having a characteristic of converting to a density level that does not perform, and block division means for dividing into a plurality of blocks by dividing at a position where image data is recorded so that one block is composed of a plurality of pixels. Density for recording dots according to the density level of image data according to the conversion characteristics that correspond to different conversion characteristics depending on the pixel position in the block The image forming apparatus is configured by a recording unit that determines a level and changes the dot size according to the density level to perform recording.

(Operation) With the above configuration, when the density level of the image data is a low density level where the visual resolution is not high, for the pixel corresponding to a specific position in the block divided by the block dividing means, The density level for converting the density level of the image data to the density level that does not record dots, and for the pixels corresponding to the positions other than the specific position in the block, the density level for recording the dots When the density level of the image data is a high density level with high visual resolution,
The density level of the image data can be converted into the density level for recording dots for all the pixels in the block divided by the block dividing means.

(Example) Next, the Example of this invention is described with reference to drawings. FIG. 1 is a schematic diagram of an image forming apparatus according to the present embodiment. In FIG. 1, reference numeral 1 is a digital data output device as an image data output device, and a digital data output device from an image scanner, a video camera or the like not shown. Image data is input, and A / D conversion and predetermined image processing are performed. In this case, the image data may be temporarily stored in the memory or may be an interface of the image data directly from the communication means. Reference numeral 2 is a gradation processing device for inputting image data from the digital data output device 1 to perform gradation processing, and 3 is a laser beam printer as a printer for inputting image data subjected to gradation processing by the gradation processing device 2. is there.

FIG. 2 shows the configuration of the gradation processing device 2. In FIG. 2, 21 is a horizontal synchronizing signal generating circuit for outputting a horizontal synchronizing signal of an image, 22 is a horizontal synchronizing signal counting circuit, Output ON-OF every time horizontal sync signal is input
F is replaced, and even line (OFF) or odd line (O
N) a horizontal binary counter for distinguishing whether the image data from the digital data output device 1 and the output signal from the horizontal binary counter 22 are used as memory addresses to perform gradation conversion, and gradation conversion having a pixel level It's a table.

Here, the gradation conversion table 23 will be described in more detail with reference to FIGS. 3 and 4. FIG. 3 shows the contents of the gradation conversion table 23. If the input image data is 8 bits (256 levels), 256 addresses are required in the table to represent one gradation characteristic. In the present embodiment, 2 addresses of even lines and odd lines are used.
Since it has one gradation characteristic, a total of 512 addresses are required. That is, the address OOH-FFH represents the gradation characteristic of even lines, and the address 1OOH-1FFH represents the gradation characteristic of odd lines.

FIG. 4 is a graph showing the gradation conversion characteristics.
When the image density is low, the pixels of the odd line are not printed and the dot size of the pixels of the even line is adjusted to reproduce the gradation. When the image density is high, the dots of the even line pixels are saturated. Print with and adjust the dot size of the pixels of the odd line to reproduce the gradation.

That is, two pixels of even lines and odd lines that are adjacent to each other in the horizontal direction are set in one block, and the characteristics of the gradation conversion table are set so that the pixels of the even lines are preferentially grown for the recording dots. In particular, in an electrophotographic printer, it is better to preferentially grow the dots of specific pixels rather than uniformly grow the dots of each pixel in the micro area of the electrostatic latent image on the photoconductor. An electric field is generated and the gradation of the recorded image is improved.

In the present embodiment, the size of the block is described as two pixels in the horizontal direction for the sake of simplicity. However, the size is not limited to this, and it can be set to any size, and the priority within the block can be set. The number of pixels for dot growth is not limited to one and may be plural.

Next, regarding the laser beam printer 3 of FIG.
This will be described in detail with reference to FIGS.

FIG. 5 is a side sectional view of the laser beam printer 3, FIG. 6 is an operation explanatory diagram of the photosensitive member reference detection, and FIG. 7 is an operation explanatory diagram of the intermediate transfer member reference detection.

In FIG. 5, 101 is a photoreceptor in which a photosensitive layer such as selenium (Se) or an organic photoconductor (OPC) is applied in a thin film on the outer peripheral surface of a belt base material such as a closed loop resin having a joint 101a. And is supported by the two photoconductor transport rollers 102 and 103 and driven by a drive motor (not shown) to rotate in the direction of arrow A.

Around the photoconductor 101, a charger 104, an exposure optical system 105, a block (B), in the order of the photoconductor rotating direction indicated by an arrow A,
Cyan (C), magenta (M), and yellow (Y) developing devices 106B, 106C, 106M, 106Y, and intermediate transfer body units
107, a photoconductor cleaning device 108, a static eliminator 109, and a photoconductor reference detection center 110 are provided.

The charger 104 includes a charging wire 111 made of a tungsten wire or the like, a shield plate 112 made of a metal plate, and a grid plate.
It is composed of 113.

The developing devices 106B, 106C, 106M and 106Y for the respective colors store toners corresponding to the respective colors. To select the color of the toner, the separating / contacting cams 115B, 115C, 115M, and 115Y whose both ends are rotatably supported by the body of the machine corresponding to the respective colors rotate in response to the color selection signal. Is brought into contact with the photoconductor 101. The remaining unselected developing units 106C, 106M, and 106Y are separated from the photoconductor 101.

The intermediate transfer body unit 107 includes a seamless loop belt-shaped intermediate transfer body 116 made of a conductive resin and the like, an intermediate transfer body transport roller 117 supporting the intermediate transfer body 116,
118, and an intermediate transfer roller 119 arranged to face the photosensitive member 101 with the intermediate transfer member 116 interposed therebetween for transferring the toner image on the photosensitive member 101 to the intermediate transfer member 116. Here, the surface perimeter L1 of the photoconductor 101 is the surface perimeter L2 of the intermediate transfer member 116.
Nominally equal, but always L1
It is set so that the relationship of ≦ L2 holds.

Reference numeral 122 denotes an intermediate transfer member cleaning device for scraping off the residual toner on the intermediate transfer member 116, which is separated from the intermediate transfer member 116 while a composite image is formed on the intermediate transfer member 116 and is used for cleaning. Abut only when serving. Reference numeral 123 is a transfer body cassette that stores a transfer material 124, and the transfer material 124 is a half-moon-shaped feed roller from the transfer material cassette 123.
The sheets 125 are sent one by one to the sheet conveying path 126.

Reference numeral 127 denotes a registration roller for temporarily stopping and waiting the transfer material 124 in order to match the positions of the transfer material 124 and the composite image formed on the intermediate transfer body 116.
Is in pressure contact with.

Reference numeral 129 denotes a transfer material 12 which is a composite image formed on the intermediate transfer member 116.
4 is a transfer roller for transferring, and the composite image is a transfer material 1
Only when transferred to 24, the intermediate transfer member 116 contacts and rotates.

Reference numeral 130 denotes a fixing device including a heat roller 131 having a heat source inside and a pressure roller 132, and the combined image transferred onto the transfer material 124 is pressed and heated by the pinching rotation of the heat roller 131 and the pressure roller 132. Then, it is fixed on the transfer material 124 to form a color image.

In FIG. 6, 110 is a photoconductor reference detection sensor for detecting the position of the seam 101a of the photoconductor 101, and is a photoconductor reference mark 101b such as a slit arranged at a predetermined position with respect to the seam 101a of the photoconductor 101. To detect. Reference numeral 121 denotes a photoconductor clutch mechanism that controls the rotation of the photoconductor by turning on and off power from a drive source (not shown).
It is provided on the drive shaft of 103.

In FIG. 7, 120 is an intermediate transfer member reference detection sensor for detecting the reference position of the intermediate transfer member 116.
The reference position is detected by an intermediate transfer member reference mark 116a such as a slit arranged at one end of 116.

With the above device configuration, the photosensitive member 101 and the intermediate transfer member 116 are
Are each driven by a drive source (not shown), and are controlled so that their peripheral speeds are the same constant speed. Incidentally, the intermediate transfer body 116 has an image forming area set in advance by the intermediate transfer body reference detection center 120 for detecting the intermediate transfer body reference mark 116a for determining the reference position, and the seam of the photoconductor 101 is set in this area. The position of 101a is adjusted so that they do not overlap with each other at the intermediate transfer roller 119, and they are driven in synchronization.

In this state, first, a high voltage is applied to the charging wire 111 in the charger 104 connected to the high voltage power source to cause corona discharge, and the photoreceptor 1
The surface of 01 is uniformly charged to about -700v to -800v.

Next, the photoconductor 101 is rotated in the direction of arrow A, and the uniformly charged surface of the photoconductor 101 is exposed with an exposure light beam 114 of a laser beam corresponding to a predetermined black (B) of a plurality of color components. When the light is irradiated from the optical system 115, the electric charge disappears in the irradiated portion of the exposure light beam 114 on the photoconductor 101, and an electrostatic latent image is formed.

At this time, the electrostatic latent image is formed on the photosensitive member 101 at a position in the image area on the intermediate transfer member 116 which is preset by a signal from the intermediate transfer reference detection sensor 120 that detects the reference position of the intermediate transfer member 116. It is formed avoiding the seam 101a.

On the other hand, the developing device 106B in which the black toner contributing to the development is stored is pressed in the direction of arrow B by the rotation of the separation / contact cam 115B according to the color selection signal and comes into contact with the photoconductor 101. With this contact, toner adheres to the electrostatic latent image portion formed on the photoconductor 101 to form a toner image, and development is completed. The developing device 106B which has completed the development is moved from the contact position with the photoconductor 101 to the separation position by the 180 ° rotation of the separation cam 115B.

The toner image formed on the photosensitive member 101 by the developing device 106B is transferred to the intermediate transfer member 116 by applying a high voltage to the intermediate transfer roller 119 arranged in contact with the photosensitive member 101.
Residual toner that has not been transferred from the photoconductor 101 to the intermediate transfer member 116 is removed by the photoconductor cleaning device 108,
The charges on the photoconductor 101 after the residual toner is scraped off are removed by the static eliminator 109.

Next, for example, when the color of cyan (C) is selected, the separation cam 115C rotates, and this time, the developing device 106C is pushed toward the photoconductor 101 and brought into contact with the photoconductor 101 to develop cyan (C). To start. In the case of a copying machine or printer that uses four colors, the above-described developing operation is repeated four times in sequence and the intermediate transfer member 11
Toner images of four colors B, C, M, and Y are superimposed on 6 to form a composite image.

The composite image thus formed is pressed from the sheet transfer roller 129, which has been separated so far, to the intermediate transfer member 116, and a high voltage is applied to the sheet transfer roller 129, so that the sheet transfer path from the transfer material cassette 123 is conveyed. It is collectively transferred to the transfer material 124 sent along 126. In this way, the transfer material 124 to which the toner image is transferred is sent to the fixing device 130, where it is fixed by the heat of the heat roller 131 and the holding pressure of the pressure roller 132, and is output as a color image.

Residual toner on the intermediate transfer member 116 that has not been completely transferred onto the transfer material 124 by the paper transfer roller 129 is removed by the intermediate transfer member cleaning device 122. The intermediate transfer member cleaning device 122 is at a position away from the intermediate transfer member 116 until a combined image is obtained once, and the combined image is transferred to the transfer material 124 by the paper transfer roller 129 and then brought into a contact state. , The residual toner is removed. With the above operation, recording of one color image is completed, and a high quality color recorded image is obtained.

The printer is not limited to the electrophotographic system using the laser beam of the present embodiment, and may be a thermal transfer system, an ink jet system, or the like. Further, the same electrophotographic method such as an LED method or a liquid crystal shutter method may be used.

In this embodiment, a full-color printer in which gradation reproduction is important is taken as an example, but a monochrome printer may of course be used. In this embodiment, the color image is superposed on the intermediate transfer member, but it may be superposed on the photosensitive member or on the transfer paper.

(Effects of the Invention) As described above, according to the present invention, when the density level of image data is a low density level at which visual resolution is not high,
For a pixel corresponding to a specific position in the block divided by the block dividing means, the density level of the image data is converted into a density level at which dots are not recorded, and the pixel is set to a position other than the specific position in the block. For the corresponding pixel, by converting the density level of the image data into a density level for performing dot recording, the image data of the pixel corresponding to a specific position in the block can be displayed in a position other than the specific position in the block. Since recording is performed using dots corresponding to the positions of pixels other than this specific position included in the pixels corresponding to the position, when forming an image with low density, all dots have the same size according to the density. The desired density can be stably obtained and the density level of the image data becomes When the high high concentration level,
By converting the density level of the image data for all the pixels in the block divided by the block dividing means into the density level for performing dot recording, a plurality of pixels corresponding to the positions of all the pixels in the block are converted. Since dots are used for recording, when a high-density image is formed, the resolution can be made the same as the resolution of image data, and a high-quality recorded image can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram showing a gradation conversion device, FIG. 3 is an explanatory diagram of a gradation conversion table, and FIG. 4 is gradation conversion. Characteristic diagram of the table, Fig. 5 is a side sectional view of the laser beam printer,
FIG. 6 is an operation explanatory diagram of the photosensitive member reference detection, and FIG. 7 is an operation explanatory diagram of the intermediate transfer member reference detection. 1 ... Digital data output device, 2 ... Gradation conversion device,
3 ... Laser beam printer.

Continuation of front page (56) Reference JP-A-2-212172 (JP, A) JP-A-60-240277 (JP, A) JP-A-59-41968 (JP, A) JP-A-62-188556 (JP , A)

Claims (1)

(57) [Claims] 1. An image forming apparatus for performing gradation recording by changing the size of each dot based on input image data, and for performing dot recording at the density level of the image data. Of the plurality of different conversion characteristics, one of the plurality of conversion characteristics is converted to a density level in which no dot is recorded when the density level of the image data is a low density level. Conversion processing means having characteristics, block division means for dividing the image data into positions to record the image data so that one block is composed of a plurality of pixels, and pixel positions in the blocks Corresponding to the conversion characteristics different from each other, and the density level for performing dot recording according to the density level of the image data according to the conversion characteristics. Because the image forming apparatus characterized by comprising a recording means for performing recording changing the size of dots in accordance with the density level.